Method for enabling interoperability between data transmission systems conforming to different standards

ABSTRACT

Mechanisms, in a transmission channel shared by 802.11 systems and HIPERLAN/2 systems are provided to prevent 802.11 terminals from transmitting during time periods allocated to HIPERLAN, so that a single channel can be shared between the two standards. In a particular embodiment, a “super frame” format is used where HIPERLAN transmissions are offered the highest level of protection possible within 802.11, which is needed within the 802.11 Contention Free Period (CFP).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/246,584 filed Oct. 7, 2008, which is a continuation of U.S. patentapplication Ser. No. 11/212,946 (U.S. Pat. No. 7,460,501), filed Aug.26, 2005, which is a continuation of U.S. patent application Ser. No.10/045,980 (U.S. Pat. No. 7,031,274), filed Jan. 1, 2002, which claimsthe benefit of provisional application 60/261,935 filed Jan. 16, 2001,the disclosures of all of which are incorporated herein by reference intheir entirety.

FIELD OF THE DISCLOSURE

This invention relates to data transmission systems and to theircontrolling operating standards. It is also concerned with wirelesslocal area networks (WLAN) and with allowing operability between twostandards.

BACKGROUND

Wireless data transmission is a rapidly growing field. One increasinglypopular form of such transmission is wireless local areas networks(WLANs). A number of standards currently exist for WLANs. However, theytend to be fragmented and largely incompatible. There is a desire for aworldwide standard that would allow a single device to functionvirtually anywhere in the world providing high-speed connectivity.

WLANs require specific protocols to transmit information, as do wiredLANs. With numerous stations along a network, LAN stations must takecare to prevent collisions if more than one station wishes to transmitinformation in the LAN. The situation is more critical in the wirelessenvironment (i.e., WLANs) since wireless stations and wireless accesspoints behave differently from wired stations.

Recently, bands have opened up between 5 and 6 GHz, which may permit aworldwide standard. Wireless standards are being developed to utilizethose bands. One such standard is HIPERLAN/2 (High Performance RadioLocal Area Network Type 2), which is of European origin. Another suchstandard is IEEE 802.11 a, which originates primarily in the US. Japanis developing standards similar to both those in the US and Europe. Boththe US and European standards profess similar levels of performance, anduse very similar waveforms to communicate. However, the two standardsare currently incompatible—Particularly at the Media Access Control(MAC) layer. As such, a large push has developed to create a singlehybrid standard, or provide some means for the two standards to easilyintemperate.

Many situations occur where 802.11a WLANs must substantially coexistwith HIPERLAN WLANs. Since they operate at overlapping frequencies,contention collisions are frequent and must be resolved if the twosystems are to operate without interference in close proximity to eachother.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of WLAN systems where interoperability isdesirable;

FIG. 2 is a block schematic of a wireless station or access point usedin the WLANS;

FIG. 3 is a graph of transmission states in the channels of a WLAN inone previously proposed solution concerning interoperability;

FIG. 4 is a graph of a proposed superframe structure of a contentionarrangement for permitting interoperability between 802.11 a WLANS andHIPERLAN WLANS;

FIG. 5 is graph of an alternative proposed superframe structure of acontention arrangement for permitting interoperability between 802.11 aWLANS and HIPERLAN WLANS.

DETAILED DESCRIPTION

Mechanisms, in a transmission channel shared by 802.11 systems andHIPERLAN/2 systems are provided in accord with the exemplary embodimentsto prevent 802.11 terminals from transmitting during time periodsallocated to HIPERLAN, so that a single channel can be shared betweenthe two standards. In a particular embodiment, a “super-frame” format isused where HIPERLAN transmissions are offered the highest level ofprotection possible within 802.11, which is provided within the 802.11Contention Free Period (CFP).

WLANs are essentially a wireless replication of a wired LAN and in manyways operated in substantially the same manner. There are importantdifferences that must be accommodated. A wireless node is unable tolisten while it is transmitting and wireless media are more likely tocontain noise and interference than are wired media. Additionally someterminals remain hidden to other terminals even though both may access aparticular network. Hidden terminals coupled with an inability of atransmitting terminal to listen may result in collisions as more thanone terminal may transmit in the same time interval.

Standards have evolved to avoid such collisions in WLANs. 802.11 is onestandard in use in North America and has probable use in Europe andother areas in the world. HIPERLAN is a similar standard for WLANs usedin parts of Europe and potentially in North America. It is notunexpected that in some areas there may exist a need to intemperate802.11 and HIPERLAN/2 systems. Both standards operate in a frequencyrange that is overlapping hence unless steps are taken to preventcollisions they will likely occur.

A typical WLAN arrangement is shown in the FIG. 1 wherein several WLANs101, 103 and 105 which may overlap are shown in close proximity to oneanother. Each WLAN includes a plurality of stations 111, 113 and 115through which messages may be sent to and received from that particularWLAN 101, 103 and 105. Each WLAN includes connection to an access port(AP) 112, 114 and 116, which permits communication between WLANs.

WLANs are accessed through stations that operate as the access ports(AP) 112, 114 and 116. AP's provide communications with services andstations outside the immediate set of wireless stations with which itcommunicates. The service “behind” the AP is termed the DistributionService (DS) in 802.11. Stations in systems using either or both 802.11and HIPERLAN/2 protocols should accommodate both. Due to the wirelessnature of the WLAN, ordinary stations need not support both systemsalthough such abilities would be desirable since it is most likely thatcommon frequencies will be shared. It is clearly desirable that the Apssupport both standards (i.e., with a hybrid AP (HAP)).

An illustrative example of a station/access port 201 is shown in theFIG. 2 and includes a wireless antenna 203, a radio signal processingcomponent 205, and a data processing component 207. The data processingcomponent receives data entered from a computer unit and transmitsreceived data from the radio unit to a computer unit of the WLAN. TheSTA/AP may take many varied forms known to those skilled in the art andhence need not be disclosed in detail.

Some prior solutions to the problem of collisions between competingsystems sharing a common frequency band have relied on a spoofingtechnique to spoof terminals into thinking that the media was busyduring a time period identified by a duration field defined by the802.11 standard. 802.11 STAs have a mechanism called the NetworkAllocation Vector (NAV) that can be set to prevent the STA fromtransmitting. However, the NAV is set only under very specificconditions that do not exist at the time the HIPERLAN/2 frames need toseize the medium. Many existing STA cannot be modified to set the NAVbased on the detection of HIPERLAN/2 transmissions. A network allocationvector (NAV) normally is set to indicate that a media is busy even if nosignal is detected. Hence setting of the NAV may be used to inhibitunwanted transmissions in cases where they might interfere with othertransmissions that are undetectable to the potentially interferingstation. Possible spoofing frames/frame sequences that could be usefulinclude a CTS transmitted by an AP, a data frame transmitted by an AP,an RTS transmitted by an AP followed by a CTS from a station, the priorRTS/CTS combination followed by an additional CTS frame from the AP, orthe prior RTSICTS combination followed by a data frame. Other framesequences can also be used with this regard.

In the system shown in FIG. 3, there is no provision to set a NAV toproperly cover HIPERLAN/2 transmissions. The solution, shown in FIG. 3,discloses a prior super-frame proposal. The problem is that there isnothing in the proposal that would force 802.11 a STA to ceasetransmissions during the HIPERLAN phase of the Superframe. The 802.11 aSTA would view the HIPERLAN phase as a part of the 802.11 ContentionPeriod (CP), and would normally be free to transmit during the CP.

A modified solution such as shown in the FIG. 4 allows a HAP to transmita spoofing frame with a duration field set to protect transmissions fromHIPERLAN/2 stations. The modified system requires no changes to anylegacy (old existing type) STA.

In accord with principles of the invention, a Super-frame structure,shown in FIG. 5 depicting signals of both standards, in a channel, isdisclosed herein that allows 802.11 a stations (STA and AP) to share asingle channel with HIPERLAN/2 stations. HIPERLAN/2 transmission occurswithin the HIPERLAN/2 phase that is buried within the Contention FreePeriod (CFP) of 802.11. The CFP occurs with a regular period, and all802.11 terminals set their NAV's during the CFP. To realize such a superframe the following sequence of frames/phases can be used as shown inthe graph of FIG. 5.

CFP Beacon, 802.11 Broadcast, 802.11 CFP, HIPERLAN/2 phase, CF End,802.11 CP

Here, CFP Beacon is a Beacon starting a CFP. Not all Beacons need starta CFP. However, the CFP must recur every integral number of Beacons. Theinference is that the Beacon period must be a sub multiple of the superframe size (which is still2k time 2 msec). For the method of FIG. 5,three phases exist. A phase here means a collection of frames primarilycontrolled by a common coordination or access function. The first phasewould consist of the CFP Beacon, 802.11 Broadcast, and 802.11 CFP. Thesum time occupied by this phase is an integral number times 2 msec, andthat number is specified as 1 for this illustrative example. Also notethat the term “Broadcast” here is used in a generic nature meaningBroadcast and Multicast frames. The HIPERLAN/2 phase would remain at ntimes 2 msec, and the CF End, 802.11 CP would have to be m times 2 msec.The sum l+m+n must be 2^(k). Note that from an 802.11 perspective, alltransmissions from the CFP Beacon to the CF End (including those fromHIPERLAN stations) would be considered as the 802.11 CFP. While the APwould restrict all CFP data transmissions to occurring in the first“Phase” of the superframe, the 802.11 stations operating in thisstructure would be unaware of the “Phases” and would only see one largeCFP, with part of it full of undetectable transmissions (the HIPERLAN/2transmissions).

FIG. 5 is meant to be illustrative of the advantages of nesting theHIPERLAN/2 phase within the CFP, rather than the CP. It represents themost limiting interpretation of the existing 802.11-1999 standard, andmost restrictive CFP scheduling rules. Depending on the flexibilityavailable within the 802.11 system, other orderings of the phases underthe CFP may be possible, and would be within the spirit of thisinvention. Such orderings would have various advantages anddisadvantages.

The key issue is support for 802.11 Power Saving (PS) stations. Thesestations spend as much of their time as possible in the “dose” state,where they cannot receive or transmit frames, but consume little power.They awake every so many Beacon Intervals (the time between Beacons) tosee if there is are any pending frames for them. The Beacon framecontains a Delivery Traffic Indication Message (DTIM) element when anyassociated 802.11 stations are in PS mode. The 802.11 stations indicateto the AP how often they wake up (their listen interval). The AP bufferstraffic for each station for at least their listen interval beforediscarding it. Stations indicate what PS mode they currently are in withevery frame they transmit.

When stations in the PS mode are present, the AP is required to maintaina DTIM interval. This interval indicates the number of Beacons thatoccur between Beacons where delivery of broadcast/multicast frames willbe attempted. Beacons which announce the delivery of broadcast/multicastframes are called DTIMs. Each Beacon contains a countdown to the Beaconwhere delivery of broadcast/multicast messages will be attempted, aswell at the interval between such beacons. When Broadcast frames aredelivered in the presence of stations in the PS mode, they must bedelivered before any directed (unicast or addressed to a single station)frames. In addition, for CFP Beacon, the beacon must indicate in theDTIM element which PS stations the AP intends to poll during that CFP.That enables the PS stations to know when they must remain awake toreceive broadcast/multicast frames, or frames addressed to them.Otherwise stations only awake once per their listen interval (and at theDTIM intervals if the must receive Broadcast/Multicast messages), and goback to their dose state immediately if no frames need to be received.Note that CFP Beacons must also be DTIM Beacons, though the reverse isnot true.

Given that PS stations will be staying awake (wasting power) to receiveframes announced by the Beacon, and that broadcast/multicast messagesmust always be transferred first, the ordering of FIG. 5 is the mostobvious solution. However, nothing in the standard prevents the deliveryof HIPERLAN/2 frames before the delivery of 802.11 broadcast frames. Inaddition, during the CFP, all 802.11 stations will remain quite untilCFP max Interval regardless of whether the channel is occupied by aknown signal. They recognize the HIPERLAN/2 phase as a part of the CFP.So there is no reason why the HIPERLAN/2 phase could not be first afterthe beacon, followed by broadcast/multicast messages, and the “CFP”phase. This reordering actually provides the maximum schedulingflexibility, at the penalty of PS stations having to remain awake duringthe HIPERLAN/2 phase.

Also, while polling of 802.11 stations during the CFP needs to be inAssociation ID (AID) order (with broadcast/multicast messages being sentfirst) nothing prevents HIPERLAN/2 messages from intervening at anypoint during polling cycle of the CFP. Thus, it is possible to have abroadcast phase start immediately after the Beacon, be interrupted bythe HIPERLAN/2 phase, and then have the broadcast phase pick up againafter the HIPERLAN/2 phase completes. Or, the CFP phase could beinterrupted by the HIPERLAN/2 phase, and then continue afterwardsfollowed by the CP. To the 802.11 stations, the Broadcast phase, CFPphase, and HIPERLAN/2 phase all appear as a single CFP phase. Thus, anyordering of these phases will work, and are within the spirit of theinvention. The key is that the HIPERLAN/2 phase should occur during theCFP phase where it has additional protection from 802.11 stations sincetheir NAV's are set for the CFP.

In the graph of FIG. 5, synchronization of signaling is secured by useof the beacon frames “B” (a management frame), which define thesuperframe size or more correctly the times between CFPs. 802.11 MACaccess functions are controlled by coordination functions of which DCFis a distributed coordination function and PCF is a centralized (point)coordination function. CFP Max length is the maximum length of acontention free period within the 802.11 system whose end is marked by“E” the CF-End management frame shown occurring at less than themaximum). As shown, the HIPERLAN/2 format transmissions (H/2 MAC-frame)occur during a portion of the 802.11 CFP. The CFP period also includes a“CFP” phase (i.e., a period of time within the CFP where actual data isdelivered using the CFP's contention free protocols). Following the endof the CFP at “E” an 802.11a format CP (contention period) is activated.A management frame “X” to permit blocking and spoofing is incorporatedboth before HIPERLAN/2 transmissions and immediately before the nextsubsequent CFP Beacon “B”. If desired “X” may be incorporated on onlyone or indeed none of these intervals. Blocking and spoofing arediscussed in my co pending application discussed herein above. Hence, byembedding HIPERLAN/2 transmissions within the contention free period ofthe 802.11 a format both systems operate without interference to/fromeach other and coordinating access via a Hybrid Access Port (which knowsthe timing of both systems).

The HIPERLAN/2 phase is viewed by 802.11 terminals as part of the CFP,and accorded protection accordingly. The CFP's maximum length(determined by the parameter CFP max length) is determined by a variableregularly broadcast in Beacon messages. It is optimally set very closeto the full length of the superframe. To relinquish the time to the CP,when the CF_End is sent, all terminals automatically reset their NAY's.Normal CP transmissions would then occur. Note that additional Beaconsmight occur during the CP that do not start a new CFP. The existence ofthese Beacons may make it easier to handle broadcast traffic, and 802.11power saver terminals, but is not a requirement.

Beacon jitter may result in jitter in the superframe. IPERLAN/2 is notvery tolerant of jitter. However, by utilizing spoofing frames jitterbefore the Beacon can be controlled. Also by allowing the broadcast/CFPtraffic to be interrupted by the HIPERLAN/2 phase, it is possible toease some of the Beacon jitter restrictions while maintaining precisetiming for the HIPERLAN/2 phase. The system would schedule theHIPERLAN/2 phase to be some time after the CFP Beacon. Since the Beaconwould jitter, the time between it and the HIPERLAN/2 phase would vary.But this time could be filled with 802.11 CFP traffic. The 802.11traffic would be suspended by the AP just prior to the HIPERLAN/2 phasestart time, and would resume after the HIPERLAN/2 phase. Alternatively,the Access Port (AP) could broadcast dummy traffic just prior to the CFPBeacon preventing other traffic from seizing the medium. In addition,while it is unlikely to be needed, a spoofing frame or frame sequencecould still be transmitted prior to the HIPERLAN/2 phase if desired tofurther assure that no 802.11 STA are active during the HIPERLAN/2phase.

While this invention has been exemplified as a system for handling802.11 and HIPERLAN/2 transmissions, its principles may be applicable toother transmission systems such as Bluetooth, HomeRF or WiMedia. Suchsystems may also be known at times a Personal Area networks (PANS)rather than WLANs. These applications will be obvious to those skilledin the art.

What is claimed is:
 1. A system comprising: a memory storing computerinstructions; and a processor coupled with the memory, wherein theprocessor, responsive to executing the computer instructions, performsoperations comprising: detecting wireless communications associated witha first device and wireless communications associated with a seconddevice, wherein the first device is configured to transmit a firstwireless signal using a first access protocol, and wherein the seconddevice is configured to transmit a second wireless signal using a secondaccess protocol; responsive to the detection, generating a super framethat includes first, second and third phases, wherein the first phase isa contention free phase for transmissions according to the first accessprotocol, wherein the second phase is for transmissions according to thesecond access protocol, and wherein the third phase is a contentionphase; assembling a spoofing frame from a request to send frametransmitted by an access point associated with the first access protocolfollowed by a clear to send frame transmitted by the first device; andending the first phase by transmitting the spoofing frame.
 2. The systemof claim 1, wherein the first access protocol is an 802.11 accessprotocol, and wherein the first device is prevented from transmittingduring the second phase.
 3. The system of claim 1, wherein the secondaccess protocol is a HIPERLAN/2 access protocol.
 4. The system of claim1, wherein the third phase is initiated by a management frame thatresets a network allocation vector.
 5. The system of claim 1, whereinthe processor, responsive to executing the computer instructions,performs operations comprising preventing the second device fromtransmitting during the first phase.
 6. The system of claim 1, whereinthe processor, responsive to executing the computer instructions,performs operations comprising securing synchronization of the superframe by use of a synchronizing beacon.
 7. The system of claim 1,wherein the processor, responsive to executing the computerinstructions, performs operations comprising ending a contention freeperiod after completion of the second phase.
 8. The system of claim 1,wherein the processor, responsive to executing the computerinstructions, performs operations comprising controlling jitter byproviding beacons in the first phase.
 9. A system comprising: a memorystoring computer instructions; and a processor coupled with the memory,wherein the processor, responsive to executing the computerinstructions, performs operations comprising: detecting wirelesscommunications associated with a first device and wirelesscommunications associated with a second device, wherein the first devicetransmits a first wireless signal using a first access protocol, andwherein the second device transmits a second wireless signal using asecond access protocol; preventing the first device from transmittingduring a designated phase for transmissions that are according to thesecond access protocol; preventing the second device from transmittingduring a contention free phase for transmissions that are according tothe first access protocol; assembling a spoofing frame from a request tosend frame and a clear to send frame; and ending the contention freephase by transmitting the spoofing frame.
 10. The system of claim 9,wherein the first access protocol is an 802.11 access protocol, andwherein the second access protocol is a HIPERLAN/2 access protocol. 11.The system of claim 9, wherein the processor, responsive to executingthe computer instructions, performs operations comprising initiating acontention phase utilizing a management frame that resets a networkallocation vector.
 12. The system of claim 9, wherein the request tosend frame is received from an access point.
 13. The system of claim 9,wherein the processor, responsive to executing the computerinstructions, performs operations comprising securing synchronizationvia a synchronizing beacon for a super frame that defines the designatedphase and the contention free phase.
 14. The system of claim 9, whereinthe processor, responsive to executing the computer instructions,performs operations comprising ending a contention free period aftercompletion of the designated phase.
 15. The system of claim 9, whereinthe processor, responsive to executing the computer instructions,performs operations comprising controlling jitter by providing beaconsin the contention free phase.
 16. A system comprising: a memory storingcomputer instructions; and a processor coupled with the memory, whereinthe processor, responsive to executing the computer instructions,performs operations comprising: generating a super frame that includesfirst, second and third phases, wherein the first phase is a contentionfree phase for transmissions according to a first access protocol,wherein the second phase is for transmissions according to a secondaccess protocol, and wherein the third phase is a contention phase forthe transmissions according to the first access protocol; providingbeacons in the contention free phase; transmitting the super frame;preventing a first device that utilizes the first access protocol fromtransmitting during the second phase; assembling a spoofing frame from arequest to send frame and a clear to send frame; and ending the firstphase by transmitting the spoofing frame.
 17. The system of claim 16,wherein the first access protocol is an 802.11 access protocol, andwherein the second access protocol is a HIPERLAN/2 access protocol. 18.The system of claim 16, wherein the processor, responsive to executingthe computer instructions, performs operations comprising initiating thethird phase utilizing a management frame that resets a networkallocation vector.
 19. The system of claim 16, wherein the request tosend frame is received from an access point.
 20. The system of claim 16,wherein the processor, responsive to executing the computerinstructions, performs operations comprising preventing a second devicefrom transmitting during the first phase.